Molluscs 147 



through no larval stage, emerging per- 

 fect little replicas of their evil-looking 

 parents. 



There is enormous variation of the 

 accepted cuttle-fish form to meet special 

 conditions. Some have the web uniting 

 the arms so exaggerated as to form an 

 umbrella, whilst many deep-sea species 

 have the eyes mounted on stalks, and 

 are furnished with luminous organs. The 

 tribe is divided into ten-armed and 

 eight-armed members, the former being 

 the more numerous. One species, the 

 Pearly Nautilus, has ninety arms. All 

 save the eight-armed octopods are pro- 

 vided with a shell generally internal 

 and by the study of fossil forms we can 

 trace its development from the earliest 

 types known. Cephalopods, though 

 abundant to-day, must have been much 

 more numerous " when the world was 

 young." Certain strata, such as the 

 lias of Dorset, are largely built up of 



